Synaptic sites on reinnervated nerve cells visualized at two different times in living mice.

Synaptic boutons on the surface of identified autonomic ganglion cells were visualized by methylene blue staining at intervals of 1-2 months following denervation to assess whether regenerating axon terminals reoccupy original synaptic sites. The distribution of synapses observed on the same neuronal cell bodies was almost always different in appearance after reinnervation. These results are at odds with the conclusions of earlier workers, who have argued that mammalian neurons bear a fixed number of synaptic sites, which are reoccupied during reinnervation.